DENVER--Microsoft is in the early stages of a plan that will see virtually its entire lineup of underlying Internet services opened up to developers, the software maker made clear this week.

In addition to making available its existing services, such as mail and instant messaging, Microsoft also will create core infrastructure services, such as storage and alerts, that developers can build on top of. It's a set of capabilities that have been referred to as a "Cloud OS," though it's not a term Microsoft likes to use publicly.

"Cloud-centric is probably a better way to say it because Cloud OS makes it sound like it is only running on the cloud," said Brian Hall, general manager of Windows Live. "A lot of the data, a lot of the apps, a lot of the interesting things are on the edge. They are on the PCs. They are on the Xboxes. They are on the phones."

But, quibbles over nomenclature aside, Microsoft made clear this week that it aims to play the same role on the Internet that it plays today on the desktop--that of providing its own applications as well as the underlying plumbing and tools that developers use to build their products.

In a speech to partners at its Worldwide Partner Conference here, Microsoft Chief Executive Steve Ballmer promised that the company would be talking to developers later this year about the first version of its developer platform, some pieces of which are currently available in beta form. Hall echoed the message that Microsoft plans to open up much of the technology that powers Windows Live as well as the underlying infrastructure.

"What's ours is yours," Hall told the crowd.

The ambitious promise comes more than a year and a half after Bill Gates first announced the company's plans for Windows Live at a November 2005 event in San Francisco. Since then Chief Software Architect Ray Ozzie and a team have been working on turning Microsoft's Internet business from a series of separate services offered directly by Microsoft into a set of more unified services that can be offered either by Microsoft directly or through partners.

At this year's Mix '07 show, Ozzie, who has been crafting the Live strategy, did talk about allowing programmers access to some of its higher-level services, such as Windows Live Spaces. But he was largely silent on the topic of the underlying developer platform.

"I've nothing to announce in that realm at this time," Ozzie told CNET News.com in an interview then. "Yet, it's pretty clear that we're working on some stuff."

Late last month, Microsoft introduced two new Windows Live Services, one for sharing photos and the other for all types of files. While those services are being offered directly by Microsoft today, they represent the kinds of things that Microsoft is now promising will be also made available to developers.

Among the other application and infrastructure components, Microsoft plans to open are its systems for alerts, contact management, communications (mail and messenger) and authentication.

"Windows Live is here as a platform for our partners," Hall said. That's not exactly the case--yet. Microsoft has made a couple of pieces, such as its Virtual Earth service, available commercially. Other components are available either for broad or limited testing, while still others have yet to be offered to developers. Instant messaging, for example, will be made broadly available to developers in test form in October.

'A real computer science challenge'
One of the key challenges Microsoft faces is trying to write tools that allow developers to code in such a way that it doesn't necessarily matter if it is a phone or a PC that is accessing the service, or whether a file is stored locally or in the cloud.

"There's a real computer science challenge for abstracting all of that well, abstracting how do you find and manage devices, how do you access devices and do it in a way that is transparent to the developer," Hall said.

Hall likens it to Windows in its early days.

"A lot of what Windows was doing early on was memory management, storage, all of the things today we take for granted," Hall said. "The vast majority of developers (today), they are not thinking, 'how am I going to store this particular piece of data in memory?' It just happens. The same thing is going to happen in the mesh model."

Microsoft is also trying to make sure that its business terms are attractive enough to woo the next MySpace or YouTube to bet on its technology. It has spent months talking to existing partners, but also to venture capital firms and start-ups.

For now, Microsoft is offering up many of its services free for up to 1 million users, while saying it wants to strike some kind of deal if a service exceeds that threshold.

"If this becomes a big, big commercial success we want to have a value exchange, but we'll give you plenty of ramp room," Hall said.

As it works to build out the underlying core services, Microsoft is also offering up applications to partners, such as Windows Live Hotmail, Windows Live Messenger and the Spaces blogging tool.

Until now, most of the deals have been one-off deals that the company has had to individually negotiate. Among Microsoft's early deals are a few colleges and universities, such as the University of Pennsylvania, as well as some telecommunications firms. On Wednesday, Microsoft announced a deal with Qwest, which will offer its Internet subscribers the option of using a Qwest-branded version of Microsoft's Windows Live services.

"It was a much more custom engagement model," Hall said. "Now we are moving to a scalable come one, come all approach."